The Wikipedia article about Smartglass says that it is compatible with Halo 4 but I can't find any further information about it. Is there anything special I can do with Smartglass interacting with Halo 4?
It has a lot of cool stats and such, which can be helpful while you are playing the game if you want to know what to focus on. Especially during load screens and such. The SmartGlass app "controller" does not appear to work with the game - but beating the Didact with your smartphone was probably never in the cards anyway.
When Halo 4 is running, the version of Xbox Smartglass on Windows 8 will allow you to access your Halo 4 stats from the main app interface if your Windows 8 device supports touch.
The iPhone version of the app can access the same stats, but the Android version of the app does not have any special interaction with Halo 4.